Embodiments of the present invention generally relate to tamper detection in electronic locks. More particularly, embodiments of the present invention relate to a capacitive proximity sensor for detecting the removal of a cover plate of an electronic lock.
The operation of certain types of mechanical switches used for tamper detection for electronic locks often rely on the displacement of a component of the mechanical switch through physical engagement with an adjacent mechanism or component of the lock device. For example, certain types of lock devices may utilize a protrusion, such as, for example, a rubber stopper, that extends from a rear side of a cover plate that engages a pivotally displaceable lever arm of a mechanical switch that is mounted to a printed circuit board. Such engagement by the protrusion may displace, and hold, the lever arm to/at a particular position, such as, for example, a first position that places the mechanical switch in an open or closed positioned. When the cover plate is moved away from the mechanical switch, the protrusion may no longer engage the lever arm, thereby allowing the lever arm to be displaced to another position, such as, for example, a second position that changes the open/closed position of the mechanical switch.
As such mechanical switches rely on physical engagement and displacement of one or more components of the mechanical switch, the switches are susceptible to mechanical failure, fatigue, and/or damage. For example, improper installation of the cover plate may result in the cover plate and/or protrusion at least initially engaging the level arm of the mechanical switch in a direction and/or manner that damages the lever arm. Further, over time, the protrusion, or the connection of the protrusion to the cover plate, may deteriorate so that the protrusion ceases to effectively engage and displace the lever arm. Additionally, unauthorized removal of the cover plate may be undetected in circumstances in which the cover plate is removed in a manner that allows for the position of the lever arm of the mechanical switch to remain relatively undisturbed. Further, the inclusion of a mechanical switch and the protrusion may increase the complexity of at least assembly and component cost of the electronic lock device.